Magnetic relay



J. R. WALKER MAGNETIC RELAY May 17, 1960 2 Sheets-Sheet 1 Filed Dec. 19, 1955 INVENTOR. 14455 2 MLKA-"R 5% ATTOIPMEY J. R. WALKER May 17, 1960 MAGNETIC RELAY 2 Sheets-Shet 2 Filed Dec. 19, 1955 IN V EN TOR. 4,145 A. MIL/(,5?

3M3, CLT' L ATTOP/YEY United States Patent MAGNETIC RELAY James R. Walker, Detroit, Mich., asslgnor to Gordon H. Cork, Birmingham, Mich.

Application December 19, 1955, Serial No. 553,965 14 Claims. (Cl. 323-89) This invention relates to electrical power control devices and has for an important object the provision of an improved power relay and actuator therefore adapted to control the power through an alternating current load circuit without recourse to moving parts in either the power supply or load circuits.

Another object is to provide an improved power re-' lay and actuating means therefor which will operate indefinitely without attention or replacement of circuit components and which is accordingly particularly desirable for use in industrial or special purpose control panels where efiicient operation for extended periods of time without maintenance is critical.

Another object is to provide such a relay having an improved time response characteristic and being adapted to effect a significant power change in a load circuit within a time interval of the order of magnitude of, a single cycle of the alternating power supply after the application of an electrical actuating stimulus.

Another object is to provide an improved electromagnetic actuator which is particularly although not exclusively adapted for use with a relay of the above character, the actuator having a plurality of receptors for receiving electrical stimuli and being responsive only to the simultaneous application of a separate electrical starting stimulus to each receptor to actuate said relay to conduct a predetermined optimum load power, the actuator being responsive to application of a single electrical stopping stimulus to any one of said receptors to actuate the relay to limit the load power to a predetermined nominal value.

Still another object is to provide an improved power relay and actuator of the foregoing charactenwherein each receptor is adapted to convert to a starting condition upon the application of a starting stimulus thereto and to remain in the starting condition until a subsequent stopping stimulus is applied thereto, the relay being operative to transmit the aforesaid optimum load power only when a predetermined number of said receptors are converted to the starting condition, and being operative to limit the load power to said nominal value when less than said predetermined number of receptors are converted to the starting condition.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Fig. 1 is a schematic circuit diagram illustrating one embodiment of the present invention.

Fig. 2 is a schematic circuit diagram illustrating a modification of the means for actuating a relay of the type illustrated in Fig. 1.

Fig. 3 is a schematic circuit diagram illustrating still another modification of the present invention.

Fig. 4 is a schema-tic block diagram illustrating an application of the circuit of Fig. 3 with a plurality of receptors for receiving electrical'starting and stopping stimuli.

it is to be understood that the invention is not limited in its application to the details of construction and ar rangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terrninology employed herein is for the purpose of description and not of limitation.

Referring in more particularity to Fig. 1, an electrical load device 10 represented by an inductance and resistance in series, which might comprise an electric motor, solenoidal operating device, or other desired electrical apparatus, is powered from a suitable alternating current supply connected to the terminals 11 and 12. The load circuit comprises in addition to the load 10, a saturable reactor or a magnetic amplifier type power relay including parallel inductance coils 13 and 14 wound around magnetizable cores 15 and 16 and each being in series with one of each of the oppositely directed current rectifiers 17 and 18. The latter may comprise any suitable rectifiers known to the art and are arranged as schematically illustrated in accordance with customary practice to pass current in the direction of the arrows through coils 13 and 14 alternately on each half cycle of the supply potential. Thus during the half cycle when terminal 11 is at a positive potential, the direction of electrical current flow will be from load 10 to rectifier 18 and thence through inductance 14 to terminal 12. When the latter terminal is in the positive half cycle, the direction of current flow will be from inductance ,13 to rectifier 17 and thence through load 10 to terminal 11.

The reactor or relay system described thus far would be self saturating by virtue of the direct current components of the load current through rectifiers 17 and 18. That is, without provision to the contrary, the magnetic flux induced in cores 15 and 16 by the aforesaid D.C. components would saturate these cores and render coils 13 and 14 comparatively low impedances to alternating current in the load circuit. In order to prevent self saturation, a pair of direct current biasing inductance coils 19 and 20 wound around cores 15 and 16 respectively so as to oppose the D.C. components of inductances due to coils 13 and 14 respectively are connected to a suitable source of direct current power at terminals 21 and 22.

The polarities of paired coils 13, 19 and 14, 20 are arranged so that the magnetic flux induced in core 15 by the D.C. component of the load current through inductor 13 and rectifier 17 is opposed and substantially neutralized by the flux of opposite polarity induced in core 15 by inductance 19. Similarly, the magnetic flux induced in core 16 by the D.C. component of theload current through rectifier 18 and inductance 14 is opposed and substantially neutralized by the magnetic flux of,

opposite polarity induced in core 16 by coil 20. In consequence the reactor comprises a high impedance choke which normally represses passage of alternating current through load 10 to a nominal value insufficient to actuate the load device 10, although the low potential difference effected across load 10 by the aforesaid nominal current is useful for another purpose as described below.

In order to overcome the choking efiect or high impedance to alternating current in the reactor or relay system, a pair of inductance control coils 23 and 24 are connected in series and wound around cores 15 and 16 respectively so as to induce a magnetic flux in core 15 opposing either the D.C. flux of coil 13 or of coil 19, and also so as to induce a magnetic flux in core 16 opposing either the D.C. flux of coil 14 or of coil 20. In the present instance, the coils 23 and 24 are schematically shown as being wound to effect the opposite polarity of coils 19 and 20 respectively. Accordingly, when coils 23.

and 24 are conducting direct current as described below,

inductances 19 and 23 neutralize each other and core is self saturated by the DC. component of power supplied through rectifier 17. Similarly, inductances and 24 neutralize each other so that core 16 is self saturated by the DC. component of power supplied through rectifier: 18. In'thiscondition of thezreactor or relay system, the alternating. load current through load 10 will be at-a desiredzoptimum operating. value.

It is apparent from the. foregoing that the control-coils 23 and 24 comprise an actuating circuit for. the above described relay in the load circuit.. Also included in the actuating circuit is a variable impedancedevice connected with a power supply and having a control element responsive to. azpredeterminedelectrical control stimulus,.

such that upon application of the control stimulus the desired direct current is.conducted through coils.23 and 24. The variable impedance device can comprise a grid controlled vacuum tube or a suitable transistor device, as for example the semi-conductor or transistor 25 shown. The actuating circuit in the present instance also comprises a pair of open core transformers 26 and 27 having their primary coils connected in parallel with the AC. power. Opposite ends of the secondary coil of transformer 26 are connected with the diagonally opposite corners of a rectangular rectifier circuit .30 containing a suitable rectifier in each side similar to the rectifiers 17 and 18; The rectifiers of circuit 30 are arranged as illustrated so that positive current will flow from left to right through resistance 31. The left and right ends of resistor 31, indicated as having positive and negative potentials respectively, are connected across the diagonally opposite corners of the rectifier circuit 30 intermediate the connections with the secondary coil of transformerv 26. A similar rectifier circuit 32 having one pair of diagonally opposite corners connected to opposite ends of the secondary of transformer 27 has its other pair of diagonally opposite corners connected to opposite ends of resistor 33, the rectifiers in circuit 32 being arranged so that positive current will flow from right to left through resistor 33.

As illustrated, the negative ends of resistances 31 and 33 are connected together and their positive ends are connected to the emitter 25a and base 25b respectively of transistor 25. The collector 250 of transistor 25 extends in series through control coils 23 and 24 and thence to one corner of a rectangular rectifier circuit 34 having its diagonally opposite corner connected to emitter 25a. The rectifier circuit 34 is similar to the circuits 30 and 32 and has its diagonally opposite corners intermediate the connections with coil 24 and emitter 25a connected in parallel across load 10' as illustrated, so that the AC. potential across load 10 will effect a positive to negative potential difference between the emitter 25a and collector 25c.

Resistances 35, 36 and 37 are illustrated to represent the impedances in the circuits involved and are determined in accordance with the current conditions desired. Resistances and 36 are selected and transformers 26 and 27 are balanced so that during the normal quiescent condition of the circuit as shown, when the aforesaid nominal current is flowing through load 10, transistor 25 is maintained in a sensitive condition receptive to a comparatively small electrical actuating stimulus to increase its conduction from a few micro-amps to a number of milli-amps.

In order to actuate the relay so as to pass optimum load current, stop and start buttons 38 and 39 are provided which are connected in the present instance with magnetizable cores 40 and 41 respectively. The latter are adapted to be selectively inserted into the open centers of transformers 26 and 27 respectively against the tension of springs 42 and 43. The latter are coiled around cores 40 and 41 and seated between fixed retainers 44 and 45 and the respective buttons 38 and 39 to urge the latter normally to their retracted positions shown.

By momentarily pushing button 38 to the right, core 40 is inserted into transformer 26 to increase the magnetic coupling between the latters primary and secondary coils and thereby to increase the potential at emitter 25a with respect to base 25b. In this operation, spring 42 is compressed against retainer 44 which is fixed with respect to the transformer 26. Thus upon release of button 38, core 40 is springreturned to the retracted position shown.

Meantime, during the brief interval that core 40 is within transformer 26, the increased potential at emitter 25a enables increased conduction of transistor 25 through coils 23, 24, andrectifier34. The-resultingDC. flux induced in cores 15' and16 opposes and partially neutralizes the flux in coils 19 and 20 asaforesaid. In consequence the A.C. load current through load 10 increases slightly from the nominal value and in turn additionally raises the positive potential at emitter 25a by virtue of the feed back from rectifier 34-. The transistor current through coils 23 and 24 thus increases additionally in further opposition to coils l9 and 20, thereby-permitting a further increase in the load current and raising still higher the positive potential at emitter 25a.

The positive feed back potential at emitter 25a rapidly increases the DC. control current through coils 23 and 24 to a predetermined optimum value which substantially neutralizes the-magnetic flux of coils 19 and 20, thereby to enable self saturation of the reactor cores 15 and 16 by the DC. components of the load current through rectifiers'17 and18. The rise in load current from the aforesaid nominal value to the optimum operating condition takes place within approximately one cycle of the impressed'A.C. power at terminals 11 and 12. However, within a fraction of a cycle, the positive potential applied at emitter 25a from rectifier 34 takes over control of transistor 25. Start button 38 can then be released and core 40 retracted without affecting the conduction of transistor 25, which is now maintained by the potential feed back-from the load circuit.

The optimum operating load current will continue until stop button 39 is pushed to insert core 41 into the central opening of transformer 27 and-thereby to increase the magnetic coupling between the latters primary and secondary coils and increase the potential of base 25b with respect to emitter 25a. Conduction through transistor 25 and coils 23 and 24 is thus decreased, thereby impairing the neutralization of bias coils 19 and 20 and causing a resultant decrease of current through load 10. In consequence the feed back potential at emitter 25a from rectifier 34 is reduced and a still further reduction in the transistor current through coils 23 and 24 takes place.

It is apparent that the conditions for initiating the optimum load current are now substantially reversed and the latter rapidly drops to its nominal value, again within approximately the time of a single cycle of the impressed potential at terminals 11 and 12. When core 41 is inserted into transformer 27, spring 43 is compressed against retainer 45, which is fixed with respect to the transformer 27. Thus upon release of button 39 after reduction of the load current to the extent necessary to prevent self-excitation by feed back from rectifier 34, spring 43 will return core 41 to the retracted position shown. The load current will now remain at its nominal value until the relay is again actuated by start button 38.

Push buttons 38 and 39 can be manually actuated, or these buttons can be limit switches operated mechanically in synchronism with an industrial operation. Likewise, it is apparent that the means illustrated including transformers 26, 27 and rectifier circuits 30, 32 for applying the starting and stopping potentials at transistor 25 can be replaced by other devices known to the art for effecting such potentials.

Referringto Fig. 2, an actuating means suitable for use with a relay of the type illustrated in Fig. 1 is shown empioying a plurality of transistors in series. In the present instance two transistors are shown, although it will be apparent that additional transistors can be employed in series "in the manner described.

Inasmuch as the relay portion of the circuit of Fig. 1 to the left of points 46 and 47 can be employed with the actuator of Fig. 2, the relay portion is not repeated in the drawing. Details of the above described circuit portions involving transistor 25, rectifiers 30 and 32, transformers 26 and 27 and push buttons 38 and 39 are the same as above described, except that the collector 256 is now connected in series with the emitter 48a of the second transistor 48. The collector 480 of the latter transistor is connected to point 47 in the circuit and thence through control coils 23 and 24 in the manner above described in regard to collector 250.

An additional pair of open core start and stop transformers 49 and 50 are employed with their primary coils connected in parallel across the power source 11, 12 and with their secondary coils connected across diagonally opposite corners of the pair of rectifier circuits 51 and 52 respectively. rectifier circuit 51 intermediate the connections with the secondary coil of transformer 49 are connected to opposite ends of resistance 53. The diagonally opposite corners of rectifier circuit 52 intermediate the connections with the secondary coil of transformer 50 are connected to opposite ends of resistance 54. The rectifier circuits 51 and 52 and their associated resistances 53 and 54 are arranged similarly to the corresponding rectifier circuits and resistances 3033. The positive side of resistance 53 is connected to the collector 25a. The positive side of resistance 54 is connected through resistance 55 t0 the base 48b of transistor 48. The negative ends of resistance 53 and 54 are connected together.

Similarly to the start and stop buttons 38, 39 are start push button 56 and stop push button 57 connected to magnetizable cores 58 and 59 respectively which are yieldingly urged to their retracted positions shown by coil springs 60 and 61 confined between their corresponding push buttons and the spring retainers 62 and 63, the latter being fixed with respect to the transformers.

As before, the resistances 35, 36, and 55 are determined so thatin the quiescent state when the nominal load current is flowing through load 10, the transistors 25 and 48 are maintained in a sensitive or receptive condition ready to conduct upon the application of a comparatively small positive starting potential at the emittors 25a and 48a simultaneously. In the quiescent condition, neither transistor is conducting appreciably and the control coils 23 and 24 are substantially de-energized.

Because of the high resistance of the transistors, the circuit of Fig. 2 is preferably employed where it is desirable to hold off the optimum load current until two separate starting stimuli are applied simultaneously to the transistors, and where it is also desirable to provide for cut-off of the load current upon the application of a single stopping'stimulus selectively to either transistor. By virtue of the circuit shown, the actuation of either start button so as to insert either core 40 or 58 into the corresponding transformer 26 or 49 will apply a positive potential to the associated emitter 25a or 48a. Because of the aforesaid high resistance of the other transistor to which the starting potential is not applied, the control coils 23 and 24 will remain substantially deenergized and will not cause an increase in the load current.

Upon the simultaneous activation of both start buttons 38 and 56, both transistors will conductsimultaneously and energize control coils 23 and 24 to initiate an increase in the load current as described above. Thereupon the resulting potential feed back from rectifier circuit 34, raising the potential of emitter 25a and lowering the potential of collector 48c, will maintain conductions of both transistors after release of the push buttons 38 The diagonally opposite corners of the and 56. The load current will rapidly rise to its optimum value as described above. In this regard, it is to be noted that the positive potential applied from rectifier circuit 30 to emitter 25a is sufliciently above the positive potential applied from rectifier circuit 51 to collector 25c, so that a suitable emitter to collector potential difference will be maintained across transistor 25 to cause conduction of the latter when both push buttons 38 and 56 are actuated simultaneously.

In order to cut off the load current, it is merely necessary to actuate either stop buttons 39 or 57 so as to insert one or the other of the cores 41, 59 into the associated transformer 27 or 50. Depending upon which push button is actuated, the corresponding rectifier circuit 32 or 52 will eifect a decrease in the emitter to base potential difference of the associated transistor 25 or 48, causing that transistor to stop conducting. The high resistance of the non-conducting transistor will then block the control current through coils 23 and 24, causing a rapid drop in the load current to its nominal value as described above.

Fig. 3 illustrates a modification of the relay for supplying power to. load 10 from an AC. power source 11, 12 as in Fig. 1. The relay circuit comprising the reactor system 13-18, the DC. bias coils 19, 20, power supply 21, 22, and control coils 23, 24, transistor 25, rectifier circuit 34, and circuit impedances 35, 36, and 37, are all arranged and operable as explained above, except that no feed back is employed across the load and rectifier circuit 34 is connected across the power supply 11, 12, rather than across the load 10. Transistor 25 is biased as describedbelow so as to be in the sensitive condition receptive to the application of a slight additional positive starting potential at emitter 25a to cause a sharp rise in conduction in the collector circuit through coils 23 and 24.

The positive actuating stimulus is supplied through a binary signal receptor circuit, as for example the flipflop circuit indicated generally by the numeral 64. It can be considered that a portion of the circuit of Fig. 1, modified as explained above in regard to Fig. 3, has been removed between the points 65a and 65b and the points 66a and 66b and that the binary circuit is substituted for the portion removed. The points 65b and 66b below the binary circuit are thus connected to the positive terminals of the rectifier circuits 30 and 32 respectively of the push button start and stop circuits of Fig. 1. Accordingly, a repetition of the circuit portion including rectifier circuits 30 and 32, transformers 26 and 27, and the push button mechanism involving cores 40 and 41 is not repeated in Fig. 3.

In the binary circuit 64, the emitters 67a and 68a of the transistors 67 and 68 are connected to the positive terinal 69 of a DO. power supply having the negative terminal 70. The collector 670 of transistor 67 is connected through resistor 71 and summing resistor 75 t0 the negative terminal 70. Collector 670 is also connected through resistances 72, 73 and 74, to the positive terminal 69. Collector 680 of transistor 68 is connected through resistance 76 to the negative terminal 70 and through resistances 77, 78, and 79 to the positive terminal 69.

.Emitter 25a is connected to the binary circuit at a location 81 intermediate resistances 71 and 75 to receive a positive potential impulse upon conduction of transistor 67. The base 67b of transistor 67 is connected to a point intermediate resistances 77 and 78, whereas the base 68b of transistor 68 is connected to a point intermediate resistances 72 and 73. A suitable bias potential for the transistor base 25b is supplied by potential divider 80 across the DC. power supply 69, 70. The circuit point 65b connected to the positive terminal of rectifier circuit 30 is also connected to the binary circuit at a location intermediate resistances 73 and 74. Similarly the point 66b connected to the positive terminal of'rectifier circuit 32 is also connected to the binary circuitv at a location intermediate resistances 78' and 79.

The components of.the:binary system shownare bal anced so that either transistor67' or 68 willal'ways be conducting, the conduction. of onetransistor being. effective to block conduction ofithe other. Assuming by way of example that transistor 67 i has been causedto conduct, as for example by the actuatio'nof start button 38 to increase the positive potential ofpoirit 65bswitli respect to point 66b and stop conduction. of'tran'sistor 68 by decreasing the latters emitter to base potential difference. In consequence the emitterto' base potential drop of transistor 67 is increased to the valueatwhich. the latter conducts. Conduction of transistor 67 substantially eliminates the potential difference across resistances 73 and 174, so that the potential'diff'erence be tween emitter 68a'and base 68b is maintained belowthe conduction level for transistor 68 even after pushibutlowered to stop conduction of transistor 67 by decreasing the latters emitter to base potential difierence. In consequence the potential of base 68b is lowered with respect to emitter 68a to enable conduction of transistor 63 after stop button 39 is released. Also as soon as transistor 67 stops conducting, the potential at emitter 25a drops and in fact becomes negative with respect to base'ZSb to stop conduction of transistor 25. Coils 23 and 24 are then de-energized and the load circuit is abruptly reduced to the aforesaid nominal value as above described.

By virtue of the circuits shown, a number of the binary receptors can be employed in parallelism and selectively actuated independently of each other to start and stop the load current. A number of such circuits are illustrated in block diagram in Fig. 4 and numbered 64a, 64b and 64, each being similar to circuit 64 and having a point 81 corresponding to point 81in Fig. 3 connected through point 65a to emitter 25a and also connected through resistance 75 to the negative supply terminal 70. Each of the circuits 64a, 64b and 640 also has a pair of points 82 and 83 corresponding to points 82 and 83 in Fig. 3 and connected directly to the power supply terminals 70 and 69 respectively. Each of the circuits 64a, 64b, and 640 also has a pair of points 65b and 66b corresponding to the same points in Fig. 3 and connected to a source of electrical actuating potential indicated'generally by the numerals 84a, 84b, and 840.

The latter are independent of each other and each comprises a push button start and stop system as illus-' trated by 84 in Fig. 1, comprising the transformers 26, 27, rectifier circuits 30, 32, resistors 31, 33, start and stop push buttons 38 and 39, including the magnetizable cores 4%), 41, springs 42, 43, and spring retainers 44, 45, all arranged and operative as described above in regard to Fig. 1. It is to be understood however that operation of the actuator circuits 64a, 64b, and64c is not dependent upon the push button device shown for supplying the'actuating signal or potential stimulus, and that other sources of the actuating signal or stimulus known to the art will be-employed where desired. By suitably biasing the potentials of the emitter, base, and collector of'tran-- sister 25 asdescribed above, the latter is preset to conduct upon conduction of any predetermined number of the staring transistors 67 in the circuits 64a, 64b and 640, and to stop conducting when less than theaforesaid predetermined number of starting transistor 67 are conducting. Accordingly the system is readily adaptable for use in industrial power control panels and provides a versatile control for a relay of the type shown, whereby the load 10' can be effectively energized or de-energized by means of atnumber of independent actuating stimuli applied through the several circuits 64a, 64b and 64c.

I claim:

1. In a solid state switching device, a self-saturating reactor in an operative A.C. circuit comprising a pair of load-coils associated with magnetizable cores to effect self-saturation of the latter by the DC. components of the inductive effects of said coils, thereby to render said coils in a stable condition of low impedance to alternating current and to effect an optimum load current in said A.C; circuit, an operative biasing circuit having inductance therein associated with said cores to unsaturate the same to produce a stable condition of high impedance in said reactor and effect a reduced load current in said A.C. circuit, an operative control circuit having control inductance therein associated with said cores and being adapted to be energized to a predetermined condition to saturate said cores, variable resistance signal initiating means in said control circuit and having one resistance value when a predetermined potential difference is applied -thereacross and being effective at said resistance value to energize said control inductance to said predetermined condition, said resistance means having a second resistance value when a second potential difference is applied thereacross and being decreasingly effective to energize said control inductance upon the changing of said poten tial difference from said one to said second potential difference whereat said control inductance is substantially de-energized, potential feedback means coupling said A.C. circuit and variable resistance signal initiating means for applying said one potential difference across the latter means when said A.C. circuit is conducting said optimum load current and for applying said second potential difference across said latter means when said A.C. circuit is conducting said reduced load current, said feedback means being increasingly eifective to change said one potential difference to said second potential difference upon decreasing of the load current to said reduced value, said variable resistance signal initiating means also having a control element responsive to electrical stimuli to change the resistance of said variable resistance signal initiating means.

2. The combination in a. solid state switching device according to claim 1 wherein said control element is responsive to a predetermined electrical stimulus for changing the resistance of said variable resistance signal initiating means an incremental amount from said one resistance value toward said second resistance value, thereby in cooperation with said feedback means to effect said reduced load current, and wherein said control element. is responsive to a second predetermined electrical stimulus for changing the resistance of said variable resistance signal initiating means an incremental amount from said second resistance value toward said first named resistance value, thereby in cooperation with said feedback means to effect said optimum load current.

3. In a solid state switching device, a self-saturating reactor in an operative A.C. circuit comprising load inductance cooperable with magnetizable core means to saturate the latter by the DC. components of the load current through said load inductance and also comprising a load impedance in series with said reactor, an operative biasing circuit having inductance therein cooperable with said core means to unsaturate the latter to produce a stable condition of high impedance in said reactor and effect a reduced load current in said A.C. circuit, an operative control circuit having control inductance-therein cooperable With said core means to saturate the latter when said control inductance is energized to a predetermined condition, thereby to produce a stable condition of low impedance in said reactor and efiect an optimum load current in said A.C. circuit, variable resistance signal initiating means in said control circuit in series with said aosaasa control inductance, said variable resistance signal initiating means having a high resistance when a predetermined small potential difference is applied thereacross and being effective at said high resistance to substantially de-energize said control inductance, said variable resistance signal initiating means having a low resistance when a predetermined large potential difference is applied thereacross and being effective at said low resistance to energize said control inductance to said predetermined condition, means for applying a positive potential feedback across said variable resistance signal initiating means as a function of'the potential difference across said load impedance comprising feedback means coupling said A.C. and control circuits and being effective to apply said small potential difference across said variable resistance signal initiating means when said A.C. circuit is conducting said reduced load current and also being effective to apply said large potential difference across said variable resistance signal initiating means when said A.C. circuit is conducting said optimum load current, and said variable resistance signal initiating means having a control element responsive to electrical stimuli to change the resistance of said variable resistance means.

4. The combination in a solid state switching device according to claim 3 wherein said control element is responsive to a predetermined electrical stimulus for reducing the resistance of said variable resistance signal initiating means an incremental amount from said high resistance, thereby in cooperation with said feedback means to effect said optimum load current, and wherein said control element is responsive to a second predetermined electrical stimulus f'or increasing the resistance of said variable resistance signal initiating means an incremental amount from said low resistance, thereby in co operation with said feedback means to effect said reduced load current.

5. In a power relay, a self-saturating reactor in anv operative A.C. circuit comprising load inductance cooperable with magnetizable core means to saturate the latter by the DO. components of the load current through said load inductance and also comprising a load impedance in series with said reactor, an operative biasing circuit having inductance therein cooperable with said core means to unsaturate the latter and effect a reduced load current in said A.C. circuit, an operative control circuit having control inductance therein cooperable with said core means to saturate the latter when said control inductance is energized to a predetermined condition, thereby to effect an optimum load current in said A.C. circuit, a plurality of variable impedance signal initiating means in said control circuit in series with each other and with said control inductance, each variable impedance signal initiating means having a high impedance when a predetermined small potential difference is applied thereacross and being effective at said high impedance to substantially de-energize said control inductance, each variable impedance having a low impedance when a predetermined large potential difierenceis applied thereacross, said plurality of variable impedance means being cooperable with each other when each is at its low impedance to energize said control inductance to said predetermined condition, means for applying a positive potential feedback across said series of variable impedance signal initiating means as a function of the potential difference across said load impedance comprising feedback means coupling said A.C. and control circuits and being effective to apply said small potential difference across said series of variable impedance signal initiating means when said A.C. circuit is conducting said reduced load current and also being effective to apply said large potential difference across said series of variable impedance means when said A.C. circuit is conducting said optimum load current, and each variable impedance means having an independent control element responsive to electrical stimuli to change the impedance of said variable impedance means.

6. In a power relay, a sell-saturating reactor inarl operative A.C. circuit comprising load inductance co-,

operable with magnetizable core means to saturate the latter by the D.C. components of the load current through said load inductance and also comprising a load impedance in series with said reactor, an operative biasing circuit having inductance therein cooperable with said core means to unsaturate the latter and effect a reduced load current in said A.C. circuit, an operative control circuit having control inductance therein cooperable with said core means to saturate the latter when said control inductance is energized to a predetermined condition, thereby to effect an optimum load current in said A.C. circuit, a plurality of variable impedance signal initiating means in said control circuit in series with each other and with said control inductance, each variable impedance signal initiating means having an independent control element responsive to one electrical stimulus to effect a low impedance value for its associated variable impedance signal initiating means and being responsive to a second electrical stimulus to effect a high impedance value for its associated variable impedance signal initiating means, each variable impedance signal initiating means being effective at its high impedance value to de-energize said control inductance, and said plurality of variable impedance signal initiating means being cooperable to effect energizing of said control inductance to said predeter mined condition when each is at its low impedance value simultaneously with the others.

7. The combination in a power relay according to claim 6 and comprising in addition a plurality of independent means associated with said plurality of variable impedance signal initiating means respectively, each being independently operative for selectively applying said one or second stimulus to its associated variable impedance signal initiating means.

8. In a solid state switching device, a self-saturating reactor in an operative A.C. circuit comprising load inductance cooperable with magnetizable core means to saturate the latter by the DC. components of the load current through said load inductance and also comprising a load impedance in series with said reactor, an operative biasing circuit having inductance therein cooperable with said core means to unsaturate the latter and effect a stable condition of high impedance in said reactor and a reduced load current in said A.C. circuit, an operative control circuit having control inductance therein cooperable with said core means to saturate the latter when said control inductance is energized to a predetermined condition, thereby to effect a stable condition of low impedance in said reactor and an optimum load current in said A.C. circuit, variable resistance signal initiating means in said control circuit and having a control element selectively responsive to one or to a second elecvtrical stimulus to effect one or a second condition of saturate the latter by the DC. components of the load current through said load inductance to produce a stable condition of low impedance in said reactor and also cornprising a load impedance in series with said reactor, an operative biasing circuit having inductance therein cooperable with said core means to unsaturate the latter to produce a stable condition of high impedance in said reactor and effect a reduced load current in said A.C. circuit, an operative control circuit having control inductance therein cooperable with said core means to saturate the latter when said control inductance is energized to a predetermined condition, thereby to effect an optimum load current in said A.C. circuit, variable resistance signal initiating means in said control circuit in series with said control inductance and having a control element selectively responsive to one or to a second electrical stimulus to effect a low or high resistance condition correspondingly for said variable resistance signal initiating means, the latter being operative at said low resistance condition to effect energizing of said control inductance to said predetermined condition and being operative at said high resistance condition to effect substantial deenergizing of said control inductance.

10. The combination in a solidstate switching device according to claim 9 and comprising in addition means for selectively applying said one or second stimulus to said control element, the latter means comprising a bi-stable flip-flop actuating circuit coupled with said control circuit and effective in one condition of stability to apply said one stimulus to said control element and being effective in its second condition of stability to apply said second stimulus to said control element.

ll. The combination in a solid state switching device according to claim 10 wherein said flip-flop circuit comprises positive and ne ative DC. power supply terminals, positive and negative stimulus out-put terminals connected to said control circuit to impart starting and stopping stimuli thereto, starting and stopping semi-conducting devices, each of said devices having, an associated emitter, collector, and base, each emitter being connected to the positive power supply terminal, a summing resistor having positive and negative ends connected to the positive output terminal and to the negative power supply ter minal respectively, a circuit portion connecting the col lector of the starting semi-conducting device to said pos'r tive out-put terminal to impart a positive potential stimulus thereto when the latter device is conducting a predetermined emitter to collector current, a second circuit portion connecting the collector of the stopping semiconducting device to said negative power supply termi nal, a separate biasing resistance associated with the collector of each semi-conducting device, each biasing resistance connecting the associated collector to said positive power supply terminal and being effective to impart a predetermined negative potential bias to the associated collector when the emitter-collector circuit of the associated semi-conducting device is in non-conducting condition, the base of each semi-conducting device being connected to the biasing resistance associated with the other semi-conducting device at a point spaced from the-positive power supply terminal by at least a portion of the latter biasing resistance, the conduction ofthe predetermined emitter to collector current by either semi-conducting device being effective to substantially short its associated biasing resistance and thereby to raise the potential of the base of the other semi-conducting device with respect to the latters emitter to render the emitter-cob lector circuit of the latter device in non-conducting condition, the emitter-collector circuit of either semi-conductor in the non-conducting condition in cooperation with the associated biasing resistance being effective to lower the potential of the base of the other semi-conducting device with respect to the latters emitter to effect said predetermined emitter to collector current in the latter semi-conducting device, a potential divider connected across said power supply terminals, said potential divider having a point connected to the negative output terminal and being effective to raise the potential of the latter with respect to the positive out-put terminal when the emitter-collector circuit of said stopping semiconducor is in non-conducting condition, and input terminals connected to said biasing resistances respectively at locations spaced from said positive power supply ter- Initial by at least a portion of the connected biasing resistance and being effective for selectively decreasing the positive to negative potential difference between the emitter and base of either semi-conducting device to render the latters emitter-collector circuit in non-conducting conducting condition upon the application of a predetermined potential difference across said input terminals, thereby to render the emitter-collector circuit of the other semi-conductor in conducting condition.

12. A bi-stable flip-flop actuating circuit comprising positive and negative DC. power supply terminals, positive and negative stimulus out-put terminals, starting and stopping semi-conducting devices, each of said devices having an associated emitter, collector, and base, each emitter being connected to the positive power supply terminal, a summing resistor having positive and negative ends connected to the positive out-put terminal and to the negative power supply terminal respectively, a circuit portion connecting the collector of the starting semiconducting device to said positive out-put terminal to impart a positive potential stimulus thereto when the latter device is conducting a predetermined emitter to collector current, a second circuit portion connecting the collector of the stopping semi-conducting device to said negative power supply terminal, a separate biasing resistance associated with the collector of each semi-conducting device, each biasing resistance connecting the associated collector to said positive power supply terminal and being effective to impart a predetermined negative potential bias to the associated collector when the emitter-collector circuit of the associated semi-conducting device is in non-conducting condition, the base of each semi-conducting device being connected to the biasing resistance associated with the other semi-conducting device at a point spaced from the positive power supply terminal by at least a portion of the latter biasing resistance, the conduction of the predetermined emitter to collected current by either semi-conducting device being effective to substantially short its associated biasing resistance and thereby to raise the potential of the base of the other semi-conducting device with respect to the latters emitter to render the emitter-collector circuit of the latter device in non-conducting condition, the emitter-collector circuit of either semi-conductor in the non-conducting condition in cooperation with the associated biasing resistance being effective to lower the potential of the base of the other semi-conducting device with respect to the latters emitter to effect said predetermined emitter to collector current in the latter semi-conducting device, a potential divider connected across said power supply terminals, said potential divider having a point connected to the negative out-put terminal and being effective to raise the potential of the latter with respect to the positive out-put terminal when the emitter-collector circuit of said stopping semi-conductor is in non-conducting condition, and input terminals connected to said biasing resistances respectively at locations spaced from said positive power supply terminal by at least a portion of the connected biasing resistance and being effective for selectively decreasing the positive to negative potential difference between the emitter and base of either semi-conducting device to render the latters emitter-collector circuit in non-conducting condition upon the application of a predetermined potential difference across said input terminals, thereby to render the emitter-collector circuit of the other semi-conductor in conducting condition.

13. In a solid state switching device, a self-saturating reactor disposed in a load circuit and including a control winding; variable resistance signal initiating means external to said reactor, said variable resistance signal initiating means arranged to supply current from at least a portion of the load circuit to the control Winding of said reactor; control means adapted to selectively supply an electrical stimulus to said variable resistance signal initiating means to' place it in a low resistance state so it can initiate a signal and supply positive feedback current to said control winding to render the reactor in a first stable state of impedance; and stopping means adapted to place the variable resistance signal initiating means in a high resistance condition, cutting ofi the positive 5 feedback and causing a second stable state of impedance in said reactor diiferent from said first state.

14. In a solid state switching device, a self-saturating reactor disposed in a load circuit and including a control winding; variable resistance signal initiating means external to said reactor, said variable resistance signal initiating means arranged to supply current from at least a portion of the load circuit of said reactor to said control winding; control means adapted to selectively supply an electrical stimulus to said variable resistance means to place it in a low resistance state so it can initiate a signal and supply positive feedback current to said control winding to render the reactor in a stable low impedance state; stopping means adapted to place the variable resistance signal initiating means in a high resistance state, cutting off the positive feedback and causing a stable high impedance state in the reactor.

References Cited in the file of this patent UNITED STATES PATENTS 2,126,790 Logan Aug. 16, 1938 2,605,306 Eberhard July 29, 1952 2,651,728 Wood Sept. 8, 1953 2,677,800 Phillips May 4, 1954 2,740,086 Evans et al. Mar. 27, 1956 2,772,370 Bruce et a1. Nov. 27, 1956 2,807,754 Steinitz Sept. 24, 1957 2,807,775 Schmidt Sept. 24, 1957 2,809,343 Pittman Oct. 8, 1957 2,854,620 Steinitz Sept. 30, 1958 

